Light sources and lamp types are commonly characterized and compared by their ability to translate electrical power into usable visible light. The efficiency or efficacy of a lighting system can be measured as the amount of light emitted (in Lumens) divided by the amount of electricity used (in Watts). The quality of light is often considered with respect to the colour of light emissions in terms of chromaticity or correlated color temperature, which described the color or wavelength of light emitted from the lighting system measured in Kelvin, and color rendering index (CRI), which indicates the lighting system's ability to show colors naturally (e.g. of an object) measured in percentage.
There exist a diverse variety of light sources which vary widely in their construction, efficiency, color characteristics, and lamp life. In general, a low color temperature corresponds to a red-to-yellow appearance like incandescent lamps (2700K) while white light emitted from fluorescent lamps operating at 4100K. Daylight and some incandescent lighting have a CRI of 100%, while fluorescent applications typically exhibit a CRI of 60%–70% while high intensity discharge (HID) sources are available with CRI ratings at or above 95%.
Incandescent lamps are the most familiar type of light source which produces light by using electric current to heat a metallic filament to a high temperature in a glass bulb filled with inert gas at low pressure. Advantages of incandescent lamps include low initial cost of purchase and good color qualities, optical control and versatility. However, standard Incandescent lights are the most inefficient and expensive to operate and have relatively short lamp lives. A halogen light source is a sub-type of incandescent lamps which includes a halogen element is in the filler gas and the bulb is normally made of quartz glass to withstand higher operating temperatures. Halogen lamps are considerably more expensive than standard incandescence and are primarily used in commercial applications
A fluorescent light source is a low-pressure mercury electric discharge lamp consisting of a glass tube filled with argon gas and mercury vapour. When current flows through the ionized gas between the electrodes, it emits ultraviolet radiation from the mercury arc which in turn is converted to visible light by fluorescent coating on the inside of the tube. Fluorescent light sources cost more and are less versatile than incandescence, but they are three to four times more efficient and last about 10 times longer than incandescence.
The three most common HID light sources are mercury vapour, metal halide, high pressure and low pressure sodium light sources and they vary in their construction, efficiency, color characteristics, and lamp life. In general, they all use an electric arc to produce intense light at relatively high efficiency and long service lives and HID lamps can save up 90% of lighting energy when used in lieu of incandescent lamps.
Mercury vapour lighting is the oldest type of HID lighting. Similar to the fluorescent lamps, a mercury vapour or mercury lamp produces light by passing current through the mercury vapour at pressure relatively higher than that in fluorescent lamps. Like all HID sources, mercury lamps consist of an arc tube enclosed in an outer bulb. Mercury vapor lights provide a very cool blue/green white light.
Metal halide lamps are generally similar in construction to the mercury lamps and the main difference is that the arc tube contains metallic salts (scandium and sodium) in addition to the mercury vapour and argon gas which results in higher light output, more lumens per watt, and better color rendition than mercury vapour lights. Metal halide lamps provide the best white light quality of the HIDs and has a high efficiency rating which is somewhere between 50% and 60% that of a comparable high pressure sodium system.
High pressure sodium systems provide high efficiency, lumen maintenance, and greater component life than traditional metal halide systems, but similar to mercury vapor. Conversely, high pressure sodium systems exhibit only modest color quality (distinctly golden-white) and the CRI of these systems is substantially (over three-fold) less than metal halide and closer to that of mercury vapor lamps. Low pressure sodium lamps are the most efficient light source currently available but they produce a monochromatic light and renders a yellow appearance on illuminated objects. Such lighting is preferably used where color rendering is not important.
In essence, incandescent lamps have low efficiency but very high CRI, low pressure sodium lamps have the highest efficiency values and the lowest CRI, and fluorescent and metal halide lamps exhibit moderately high efficiency and CRI.
Elongated fluorescent light fixtures and reflectors have been commonly used to provide illumination for diverse purposes. Conventionally, rectangular, dome- and arch-shaped light reflector fixtures with a cross section resembling of a conic section, have been used to house one or multiple light source(s) as exemplified in Stotter in Canadian Patent No. 682,592; Armstrong U.S. Pat. No. 4,078,169; Tickner in Canadian Patent No. 2,099,293; Swarens in U.S. Pat. No. 5,988,836; Baar in U.S. Pat. No. 6,257,735; Ruud and Lewin in Canadian Patent No. 1,076,086; Hernandez in Canadian Patent No. 1,128,482; Heider and Gurel in Canadian Patent No. 1,309,451; Shemitz in Canadian Patent No. 2,147,106; Nielson et al. in Canadian Patent Application No. 2,160,598; and Raby and Raby in Canadian Patent Application No. 2,193,787.
Acknowledging the inherent inefficiency of the above traditional light fixtures in respect of light energy loss in the area between the light source and the top surface of the light reflector, Lewin in U.S. Pat. No. 4,388,675 and Lee in U.S. Pat. No. 4,599,684 and Canadian Patent No. 1,266,850 have developed the concept of adding one or more elongated channel(s) or rib integral(s) each with a substantially V-shaped cross section to the top surface of the more conventional rectangular light housings, while DeLlano in U.S. Pat. No. 3,829,677; Douma and Brugham in U.S. Pat. No. 4,242,725; Figueroa in U.S. Pat. No. 4,499,529; Gallagher in U.S. Pat. No. 4,674,016 and Canadian Patent No. 1,259,975; Ruud and Lewin in Canadian Patent No. 1,111,818; Grenga and Eannarino in Canadian Patent Application No. 2,147,628; and Stanton & Wasney in Canadian Patent Application No. 2,297,875 essentially all taught the simple incorporation of substantially a V-shape channel or rib integral into each generally shaped parabolic reflector in a manner that said V-shaped channel is incorporated substantially at the vertex (the apex) of the parabola shaped cross section extending longitudinally along the length of the reflector with the bottom of said V-shaped channel extruding towards and running parallel the light source.
For the purpose herein, the optical center of a parabola or of any other conic section shall mean the focus of same which is a point on the principal axis of the conic section on which incident rays parallel to the principal axis either converge towards, or appear to be diverging from. The principal axis is in turn the line that passes through the vertex and the center of curvature, and is perpendicular to the focal plane. The directrix of a conic section is a line which in conjunction with the focus serve to define the conic section in that the shortest distance between any given point on the conic section and the focus is proportional to the shortest distance between said point on the conic section and the directrix. The above ratio is one if the conic is a parabola, the ratio is less than one if the conic is an ellipse, and the ratio is greater than one if the conic is a hyperbola. For greater certainty, more detailed information on conic sections can be found in Yates, R. C. “Conics.” A Handbook on Curves and Their Properties. Ann Arbor, Mich.: J. W. Edwards, pp. 36–56, 1952; Salmon, G. Conic Sections, 6th ed. New York: Chelsea, 1960; Sommerville, D. M. Y. Analytical Conics, 3rd ed. London: G. Bell and Sons, 1961; Eves, H. “The Focus-Directrix Property.” §6.8 in A Survey of Geometry, rev. ed. Boston, Mass.: Allyn & Bacon, pp. 272–275, 1965; Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, D.C.: Math. Assoc. Amer., pp. 141–144, 1967; Downs, J. W. Practical Conic Sections. Palo Alto, Calif.: Dale Seymour, 1993; and Hilbert, D. and Cohn-Vossen, S. Geometry and the Imagination. New York: Chelsea, 1999.
It should be noted that the light source, in each case, has been taught to be positioned virtually directly adjacent either to the vertex of the cross section of the reflector or to the V-shaped rib integral so that it can be substantially at the optical center of the reflector. For instance, Spitz in U.S. Pat. No. 4,719,546 teaches a fluorescent lighting conversion apparatus to enable the elimination of at least one of multiple fluorescent tubes from conventional fluorescent lighting systems and specifically teaches that the longitudinally axis of the remaining fluorescent tube must be positioned substantially in the upper half of the downward facing elongated reflector means. Furthermore, the length of the elongated light source in each case spans substantially the full length of the elongated reflector.
More recent advancements in the field are to further the efficiency of light reflectors by using increasingly reflective materials for lining the interior surface of light fixtures so to maximize expulsion of light from the fixture thereby reducing light energy loss through absorption by the reflector. For example, Crabtree in U.S. Pat. No. 4,336,576 and Spitz in U.S. Pat. No. 4,719,546 taught fluorescent lighting conversion apparati using mirror surfaces to enable the elimination of at least one of multiple fluorescent tubes that are otherwise required to be used in conventional fluorescent lighting systems. Mcllwraith in U.S. Pat. No. 6,164,800 and Canadian Patent No. 2,177,634 taught the coating of light fixtures components such as parabolic louvers with metal substrates with optically useful reflective properties. Raby and Raby in Canadian Application Patent No. 2,193,787; Forcht and Thomas in U.S. Pat. No. 4,490,184; and Tennant and Hood in U.S. Pat. No. 5,251,064 taught the use of metal-incorporated and metalized plastic films with high reflectance for lining lighting fixture reflectors.
While all of the above conventional elongated light reflectors with a parabolic cross section incorporating the V-shaped channels and increasingly reflective materials can be used to reduce primary light “trapping” and energy loss within the area between the light source and the vertex (e.g. the “roof” of parabola) of the reflector, the prior inventors neither addressed nor remedied the impact of the addition of such channels on the direction or spread of distribution, and more importantly the uniformity, of the light emitted from said parabolic fixtures.
In other words, while incorporation of a centrally disposed V-shaped channel can minimize the reflection of light directly back onto the light source (thus reducing wastage), the V-shaped channel now redirects this additional light energy (that is otherwise wasted) to exit the lighting apparatus via either side of the light source thereby invariably providing extra illumination and creating as a side effect uneven illumination usually manifested as two parallel ovoid “hot-spots” sandwiching a central darker area.
Further, none of the above prior art citations teaches specific methods to optimize the positioning of multiple light fixtures, each incorporating a centrally disposed V-shaped channel for efficiency purposes, to maximize the quality and uniformity of light emissions in a cost-effective manner for a given purpose of use or application requiring same for large target areas.